MicroRNAs (miRNAs) are short 20-22 nucleotide RNA molecules that are expressed in a tissue-specific and developmentally-regulated manner and function as negative regulators of gene expression in a variety of eukaryotes. miRNAs are involved in numerous cellular processes including development, proliferation, and differentiation [Ambros 2004; Bartel 2004; Shi et al. 2010]. Increasing evidence has linked miRNAs to cancer [Esquela-Kerscher & Slack 2006] and are important regulators of many key pathways implicated in tumor pathogenesis [Asadi-Moghaddam et al. 2010], functioning as oncogenes or tumor suppressors in various tumors [Cheng et al. 2010].
Although miRNAs have been shown to be differentially expressed in various types of cancer cells as compared to normal cells, many cancers are thought to be maintained by a population of cancer stem cells that retain stem cell properties, are highly tumorigenic, and display increased resistance to radiation and chemotherapy. As such, cancer therapies should target tumor stem cells, but spare normal stem cells. Therefore, there is a need for identifying miRNA molecules that are differentially expressed in tumor stem cell subpopulations as compared to normal stem cells for the development of miRNA-based cancer therapeutics and diagnostics.